Grigor Dimitrov was forced to rescue two match points before eventually overcoming Malek Jaziri, while Rafael Nadal had no such problems at the Barcelona Open on Thursday.
Second seed Dimitrov, aiming for just his second clay-court title and his first in four years, was taken the distance - and to the brink of a shock defeat - before completing a 7-5 3-6 7-6 (10-8) success.
The opening set proved a sign of things to come as world number 88 Jaziri took a 4-2 lead, but Dimitrov hit back and belatedly forged ahead by converting his fifth set point.
Jaziri was unbowed, however, and broke at either end of the second to level the match before once again taking a 4-2 lead in the decider, and the Tunisian earned a match point at 6-5 with Dimitrov on serve.
He could only net a backhand, though, as the Bulgarian forced a tie-break, where the drama continued.
Dimitrov wasted a trio of match points - sending a makeable backhand wide on the third - and breathed a sigh of relief when Jaziri dumped a forehand into the tramlines at 8-7. As the match approached the end of its third hour the Tunisian finally cracked, netting a forehand as his opponent squeezed into the quarter-finals.
He will play Pablo Carreno Busta, who defeated Adrian Mannarino in another match decided on a final-set tie-break.
There was no such drama later in the day as Nadal breezed past compatriot Guillermo Garcia-Lopez 6-1 6-3 to chalk up his 16th straight victory on clay, as well as extending his record of consecutive sets won on the dirt to 40. Martin Klizan awaits in the last eight.
Third seed Dominic Thiem got the better of Jozef Kovalik, while there were also wins for Stefanos Tsitsipas, fourth seed David Goffin and Roberto Bautista Agut.
Meanwhile, there was a shock at the Hungarian Open as top seed and defending champion Lucas Pouille was dumped out 6-3 6-4 by John Millman. Yannick Maden, Andreas Seppi and Nikoloz Basilashvili were Thursday's other winners in Budapest.
|WATCH: Chargers top Chiefs on dramatic two-point conversion in final seconds|
|Suns owner Sarver committed to keeping team in Phoenix|
|Chargers WR Allen leaves with injury after near-spectacular catch|
|Socceroos not giving up on Mooy for Asian Cup|
|Cooper says Raiders owner wanted to trade him to Cowboys|
|Pochettino jokes Levy is ´worried´ about losing him|
|Barcelona would welcome Morata – Alba|
|Toure not a priority for West Ham – Pellegrini|
|Koscielny no certainty to face Southampton, says Emery|
|We gifted the game – AC Milan boss Gattuso furious after Europa League exit|
|My season starts now, says Koscielny|
|Cipriani ´at peace´ with latest England snub|
|Laporte: Deschamps must have personal reasons for France snub|
|Morata injury not too serious, claims Chelsea boss Sarri|
|Hansen to leave: All Blacks coach returning focus to World Cup defence|
|I want to fight the champion! - Joshua reiterates Wilder in April ambition|
|Gundogan glad to leave Christmas holidays behind|
|I know how it feels and it hurts - Gundogan on Sterling abuse|
|Celtic 1 Red Bull Salzburg 2: Scottish champions through despite defeat|
|Olympiacos 3 AC Milan 1: Rossoneri crash out of Europa League|
|Arsenal 1 Qarabag 0: Lacazette on target as Saka shines|
|Hansen to leave: All Blacks will take time to name replacement|
|Chelsea condemn alleged anti-Semitic chanting from fans|
|Hansen to leave: The best Opta facts from New Zealand coach´s tenure|
|Hansen to leave: Five contenders to be the next All Blacks coach|
|Hansen to leave: Highs and highs of his All Blacks reign|
|Hansen to leave All Blacks after World Cup|
|Rapid Vienna 1 Rangers 0: Late Ljubicic winner sends Gerrard´s men out|
|Beckham continues to miss Giants practice with quad injury|
|Vidi 2 Chelsea 2: Giroud spares Sarri´s side in lacklustre draw|
|Paris Saint-Germain and Marseille fixtures among latest Ligue 1 cancellations|
|Santos turn to ex-Argentina boss Sampaoli|
|Muller could miss Champions League last 16 after Tagliafico kick|
|Home hope Bekker out in front at Alfred Dunhill Championship|
|Van Bommel in touch with Robben over PSV reunion|
|Pinarello chief confident over Team Sky future|
|Stade make Ospreys tickets free in tribute to teenager|
|WRC great Loeb seals Hyundai switch|
|Madrid rumours better than sack talk, says Pochettino|
|Nadal to join Federer at 2019 Laver Cup|
|Prigoda smashes world record, Hosszu dethroned in Hangzhou|
|Former Juve CEO Marotta takes over at Inter|
|Glenn to stand down as FA boss next year|
|Muller apologises to Tagliafico for kick to the head|
|Pereira pleads for more Manchester United chances|
|Griffin hails ´phenomenal´ Lowry after Warriors demolition|
|I´ve played with Zidane and Henry, but Messi is something else – Pires|
|Dragons forward Jack de Belin charged with sexual assault|
|Durant: Raptors are the real deal|
|Cocu bids farewell to Fenerbahce after ´mutual agreement´ is made over October sacking|
|Australia unchanged for historic Perth Test|
|Champions League draw: The possible last-16 ties|
|Southee happy to be back on home soil|
|I wouldn´t swap Dembele for Neymar – Pires|
|Canelo ready to risk heavy weather against Fielding|
|Raptors upstage Warriors, Davis leads Pelicans with 44 points|
|India skipper Kohli excited by green Perth wicket|
|PSG? I haven´t decided my future yet – De Jong|
|Marcelo: Real Madrid don´t have attitude problem|
|India pair Ashwin, Rohit ruled out of second Test|
|Kovac: Ajax-Bayern draw was amazing|
|Sims re-signs with Dragons until 2022|
|Derrius Guice injury update: Redskins RB (knee) has rehab setback, undergoes 3 more procedures|
|Emery: Arsenal could sign defender in January|
|Phillies sign McCutchen to three-year deal|
|O´Neal thinks his Lakers teams could ´easily´ beat Warriors|
|A-League to add two clubs by 2020|
|Curry says he was ´obviously joking´ about moon landing comments|
|Now the beautiful part starts – Ronaldo ready for Champions League knockout stage|
|Bayern have a lot more potential – Lewandowski not satisfied despite top spot|